3pc-lamfreq

3pc-lamfreq is a Python library used for free vibration analysis of shear deformable anisotropic laminates. It provides a Lamfreq class to calculate natural frequencies and mode shapes based on first-order shear deformation theory (FSDT) and classical laminate theory (CLT).

Installation

Use the package manager pip to install 3pc-lamfreq. Since the package and its dependencies are available on PyPI, you can install them directly:

pip install 3pc-lamfreq

API Reference

Lamfreq Class

The primary component of this package is the Lamfreq class, which takes a panel, a load case, and configuration parameters to perform natural frequency and vibration analysis.

from lamfreq.lamfreq import Lamfreq

Required Parameters

When initializing Lamfreq, the following parameters are required:

• panel (Panel): An instance of the Panel class (from 3pc-panel) containing the laminate definition and geometry.
• loads (Loads): An instance of the Loads class (from 3pc-loads) containing the load case and environmental conditions.
• number_of_terms (int): The number of terms to be used in the Ritz/analytical analysis.
• number_of_points_x (int): The number of grid points in the x-direction where the mode shapes are reported.
• number_of_points_y (int): The number of grid points in the y-direction where the mode shapes are reported.

Calculated Properties

The class calculates the following properties:

• NT: Thermal in-plane loads.
• NC: Hygral in-plane loads.
• pairs: List of term index pairs (i, j) for analysis.
• K33: The loads-dependent part of the stiffness matrix.
• lambdaEV: Eigenvalues of the vibration system (natural frequencies in rad/s).
• vr: Right eigenvectors (mode shapes).
• lambda_cr: Critical eigenvalue.
• vr_cr: Critical right eigenvector.
• mn_cr: Critical (m, n) pair.
• lambdaP: Sorted list of positive eigenvalues.
• lambda1 to lambda5: First five natural frequencies in Hz.
• mn1 to mn5: Dominant (m, n) mode shapes corresponding to the first five frequencies.
• loc: Grid coordinates where mode shapes are computed.
• w1 to w5: First five right eigenvectors.

Methods

Lamfreq.fromDict(**kwargs)

Initializes a Lamfreq instance using a dictionary of keyword arguments.

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Usage Examples

Basic Initialization

Below is an example of performing a vibration analysis on a panel.

from panel.panel import Panel
from loads.loads import Loads
from lamfreq.lamfreq import Lamfreq

# Assuming pnl (Panel) and ld (Loads) are already defined
lmf = Lamfreq(panel=pnl, loads=ld, number_of_terms=8, number_of_points_x=5, number_of_points_y=5)

# Access natural frequencies (in Hz)
print("First Natural Frequency (Hz):", lmf.lambda1)
print("Second Natural Frequency (Hz):", lmf.lambda2)

# Access dominant modes
print("First Dominant Mode (m, n):", lmf.mn1)

Commands

The package provides a command-line interface entry point. After installing, you can run the application using:

lamfreq input.cfg

(This entry point is defined in lamfreq.main:main)

Options

• config (positional): Specify the configuration file (.cfg) to run the analysis.
• -h, --help: Show the help message and exit.
• -v, --version: Show the version number.
• -s, --sample: Copy example files (materials, plies, laminates, panels, loads, etc.) to the current directory.

Configuration File (input.cfg)

The lamfreq command requires a configuration file (typically named input.cfg or lamfreq.cfg). Below is an example based on lamfreq/examples/composite001/lamfreq.cfg:

[files]
materials = materials.json
plies = plies.json
laminates = laminates.json
panels = panels.json
loads = loads.json
output = output.txt

[analysis]
number_of_terms = 8
number_of_points_x = 5
number_of_points_y = 5
output_K = no
output_M = no

[files] Section

This section defines the paths to the required input JSON files and the desired output file:

• materials: Path to the materials JSON file. Follows the format expected by 3pc-material.
• plies: Path to the plies JSON file. Follows the format expected by 3pc-ply.
• laminates: Path to the laminates JSON file. Follows the format expected by 3pc-laminate.
• panels: Path to the panels JSON file. Follows the format expected by 3pc-panel.
• loads: Path to the loads JSON file. Follows the format expected by 3pc-loads.
• output: Path to the text file where the vibration analysis results will be written.

[analysis] Section

This section specifies the analysis settings:

• number_of_terms: The number of terms to use in the Ritz/analytical solver.
• number_of_points_x: Number of reporting points along the length (x-axis).
• number_of_points_y: Number of reporting points along the width (y-axis).
• output_K: Option to output the stiffness matrix (yes or no).
• output_M: Option to output the mass matrix (yes or no).

Citation

If you use this library in your research or work, please cite it as follows:

APA Format:

Rastogi, N., & Seresta, O. (2026). 3pc-lamfreq: Python library for free vibration analysis of shear deformable anisotropic laminates. PyPI. https://pypi.org/project/3pc-lamfreq/

BibTeX:

@software{3pc_lamfreq,
  author = {Rastogi, Naveen and Seresta, Omprakash},
  title = {3pc-lamfreq: Python library for free vibration analysis of shear deformable anisotropic laminates},
  year = {2026},
  url = {https://pypi.org/project/3pc-lamfreq/}
}